Several systems have been developed for the use in correcting and stabilizing orthopedic injuries or deformities and promoting bone fusion. For example, in systems intended for the spine, an elongated member, commonly in the form of a bendable rod, can be longitudinally disposed adjacent the vertebral column and is fixed to various vertebrae along the length of the column by way of a number of spinal fasteners. A variety of spinal fasteners can be used, such as hooks, bone bolts and screws, each configured to engage a specific portion of the vertebrae.
An example of a spinal fixation system of this type is the TSRH® Spinal System. In this product, spinal hooks and bone screws are engaged to a spinal rod by way of eyebolts. The eyebolts and associated clamping nut provide a three-point shear clamp that positively locks the hook or screw element to the spinal fixation rod.
The TSRH® Spinal System, sold by Medtronic Sofamor Danek, includes connectors allowing variable angular, height, and axial orientations between the elongated members and the spinal fasteners. One example of such a connector is disclosed in U.S. Pat. No. 5,947,967. Embodiments of that connector allow degrees of freedom of movement in an infinitely variable fashion to help reduce difficulties in placing implants prior to and during manipulation of the spine. Such freedom during installation tends to make implantation significantly easier.
Under some conditions, a degree of back-out of the spinal fasteners can occur in some spinal systems after installation. In some cases, such back-out does not affect the performance of the implants. In other cases, however, performance of the implants may be lessened, and additional surgery may be necessary to secure or replace implant parts. Accordingly, a connecting member, such as a connector for the spine, that combines a wide range of freedom of movement between it and a fastener, with assistance in preventing back-out of fasteners after installation and simple assembly during surgery would be desirable.